Flexible, Task-Dependent Use of Sensory Feedback to Control Hand Movements

Abstract

We tested whether changing accuracy demands for simple pointing movements leads humans to adjust the feedback control laws that map sensory signals from the moving hand to motor commands. Subjects made repeated pointing movements in a virtual environment to touch a button whose shape varied randomly from trial to trial-between squares, rectangles oriented perpendicular to the movement path, and rectangles oriented parallel to the movement path. Subjects performed the task on a horizontal table but saw the target configuration and a virtual rendering of their pointing finger through a mirror mounted between a monitor and the table. On one-third of trials, the position of the virtual finger was perturbed by Ϯ1 cm either in the movement direction or perpendicular to the movement direction when the finger passed behind an occluder. Subjects corrected quickly for the perturbations despite not consciously noticing them; however, they corrected almost twice as much for perturbations aligned with the narrow dimension of a target than for perturbations aligned with the long dimension. These changes in apparent feedback gain appeared in the kinematic trajectories soon after the time of the perturbations, indicating that they reflect differences in the feedback control law used throughout the duration of movements. The results indicate that the brain adjusts its feedback control law for individual movements "on demand" to fit task demands. Simulations of optimal control laws for a two-joint arm show that accuracy demands alone, coupled with signal-dependent noise, lead to qualitatively the same behavior.

Sensory Feedback Reduces Individuality by Increasing Variability within Subjects

“…Thus, the study demonstrates the importance of determining how sensory feedback affects both within -animal and across -animal variability, rather than simply measuring the variability of a population. It also strongly supports prior work that demonstrates that one must determine the biomechanical context and the task-relevance of motor program components to understand how sensory feedback is addressed to each one [10, 21–22]. …”

Task-dependent coordination of rapid bimanual motor responses

“…Several studies examining unimanual movements have shown that feedback gains are set in a manner consistent with predictions of OFC (Franklin and Wolpert 2008; Knill et al 2011; Liu and Todorov 2007). While such studies have focused on how one arm responds when perturbed, there are many situations in which richer behavior can be seen.…”

Dynamic Multisensory Integration: Somatosensory Speed Trumps Visual Accuracy during Feedback Control

“…Previous work shows that visually guided movements are rapidly updated following changes in the visual target (Goodale et al, 1986;Prablanc and Martin, 1992;Day and Lyon, 2000), and online corrections for cursor or target jumps are modulated by the reliability of visual feedback (Körding and Wolpert, 2004;Izawa and Shadmehr, 2008). Studies have also documented that visual perturbations evoke rapid and task-dependent motor corrections during reaching (Franklin and Wolpert, 2008;Knill et al, 2011;Oostwoud Wijdenes et al, 2011). Without questioning the importance of vision, our observation that the visual perturbations did not engage any motor response suggests that the relationship between state estimation and visuomotor feedback during reaching deserves further investigation.…”